WO2012052165A1

WO2012052165A1 - Apparatus for measuring soil humidity

Info

Publication number: WO2012052165A1
Application number: PCT/EP2011/005261
Authority: WO
Inventors: Armando Carravetta; Riccardo Martino; Rosario Schiano Lo Moriello
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-10-22
Filing date: 2011-10-19
Publication date: 2012-04-26
Anticipated expiration: 2013-04-22
Also published as: IT1402413B1; ITMI20101957A1

Abstract

An apparatus for measuring soil humidity, employable in irrigation systems that provide buried pipes made of plastic material and especially in drip sub-irrigation systems, comprising a network of ducts consisting of buried rectilinear or mixed-linear development pipes, rectilinear or "T" joints, caps and eventual curvilinear elements. In the apparatus thereof, a number of rectilinear ducts consist of tubular elements (10), made of rigid or flexible plastic material of whatever suitable section, incorporating two electric cables (12-14) in conductive metal material. The tubular elements (10) are associated to rectilinear (16) or "T" (18) joints and to end caps (20-22) apt to guarantee the electric continuity of the apparatus thereof.

Description

"Apparatus for measuring soil humidity"

DESCRIPTION

This invention relates to an apparatus for measuring soil humidity.

Namely, this invention relates to an apparatus for measuring soil humidity in irrigation systems that provide buried pipes made of plastic material and especially in drip sub-irrigation systems, which are frequently employed especially in arid or semi-arid climate areas and regions in order to optimise water consumption.

As is known, ground farming of horticultural products usually requires a specific and constant irrigation contribution. Water supply, excluding rainwater, to be provided for different cultivations, varies obviously in function of several features, related to, for example, kind of buried product, soil and climate conditions. In the areas wherein water abundance, obtained both from pits and from channels deriving from watercourses, is sufficient, irrigation is performed from above, or in any case above the cultivated soil, with quantities delivered once or few times during the day. In other areas, typically arid or semi-arid, scarcity of rainfalls and limited availability of water resources to be allocated to farming forces the employment of specific irrigation forms. In some cases, there may be employed apparatus delivering water drop by drop, more or less continuously through a water network having no22les arranged on the ground in correspondence of various vegetables, groups of vegetables or plants. In other cases the buried ducts made of plastic material are provided with dripping wings which deliver water direcdy to the root apparatus area, allowing more frequent irrigation contributions without reaching a full saturation of the soil. The delivery of water performed in this way avoids a useless dispersion thereof and guarantees an optimal degree of humidity for the crops. A solution of this kind, however, abstracts from the knowledge of the properties of the soil, namely of the humidity present therein. At this regards, a technology named TDR (Time Domain Reflectometry) is employed, further than to identify partial interruption of power lines and for the indirect detection of ground subsidences caused by landslide movements, for measuring the water content of soil. The method based on said technology provides, for identifying interruptions of power lines, the sending from of a point of the electrode itself of an impulse represented by a stepped signal and consisting of a difference in potential between the two cables, as well as the measurement of the reflected signal; the deformation of the wave, determined by the total or partial interruption of the power line is interpreted to identify the position of the damage and the kind thereof. In the case of ground subsidences, caused by landslide movements, the cable is stretched or split said subsidence may be detected employing the same TDR technology.

It is known that the latter is employed as well for measuring water content of soil, by sending an electric signal sent through a fork shaped and suitably dimensioned antenna, sunk in the soil; the electric signal follows the antenna, but is diffused as well in the soil. The deformation of the wave shape, in this case, is caused by the way of propagation through the soil and is linked, namely, to the dielectric constant of the soil thereof which is, in turn, function of the water content present in the soil.

However, this known technology shows the drawback of providing only localized or punctual information, while soils have naturally variable properties and, as a consequence, the water content present therein varies from a vertical to another. In order to obtain a field scale evaluation, that is the average and the deviation in soil water content values, several probes sunk in the soil and an even more significant number of probes to obtain different evaluations for each irrigation line would be required.

A further drawback shown by this technology is related to the fact that due to the presence of a huge number of probes and irrigation lines, a localized failure of one of them may elude control and cause an excess of water in a given zone.

WO 1993/017316 describes the employment of electric cables, laid down along water ducts under construction in order to be subsequendy employed with the purpose of detecting water leaks. The wave deformation caused by the variation of the dielectric constant of the soil in correspondence of the leaks, due to a localised increase in water quantity, may be interpreted to identify the position of the leak along the ducts. This technology, on the other hand, is employed and serves only for the research of possible leaks along water ducts, not for sampling the average water content of soil.

The average measurement of the water content of a soil is also the object of US 5,942,904 through a technique providing the employment of a couple of electric cables deeply inserted in the soil. Also this measurement is based on the known principles of wave shape modification, induced by the variation of the dielectric constant of the soil wherein the cables are inserted; said variation is in turn ascribed to the variation in the water content of soil.

However, this technique shows a significant drawback, connected to the fact that the electric cables must be inserted in the soil at a given depth, typically not lower than 20-25 centimetres; this implies both the initial difficulty to house the electric cables in the soil keeping the parallelism thereof, and the risk that they may be damaged by periodical tillage of the soil itself performed by means of farming machines. Moreover, it has to be considered that the development of root apparatus may easily lead to variations in the distance between cables, impairing the possibility to calibrate the system once for all.

In drip sub-irrigation systems, furthermore, water tends easily to evaporate if it is delivered in surface; in order to obviate this drawback, irrigation water is delivered, through buried ducts, directly in correspondence of the root apparatus of the raised crop, without however knowing the average water content of soil in the respective zones.

It would be, instead, extremely useful to have such information available because it would, on one hand, allow a saving in terms of water volumes, and, on the other hand, the optimization of the quantity of water delivered to the crops in function of the humidity already present in the soil. US 6,016,971 teaches a method for controlling the irrigation of a grassy soil in function of the humidity content of the soil, through a humidity sensor providing a signal for opening a valve suitable to deliver a given quantity of water. The sensor comprises an insulating body whereto two electrodes arranged in the cap of a number of tubular ducts are connected.

US 4,952,868 discloses a soil humidity measuring device comprising a couple of concentric cylindrical conductors, separated by a layer of glass beads to form a condenser, the resistance thereof varies according to the level of humidity present in the fibrous material.

According to these solutions soil humidity control apparatus are completely independent from the irrigation systems.

The object of this invention is to obviate the drawbacks mentioned hereinabove.

Namely, the object of this invention is to provide an apparatus for measuring soil humidity, especially employable in drip sub-irrigation systems, which allows to systematically sample the measure of the humidity of soil in correspondence or in the proximity of the root apparatus of each different row of cultivated plants.

A further object of the invention is to provide an apparatus as defined above which consequendy allows to optimize the quantity of water delivered to the different plants, preventing the waste of water resources. Not secondary object of the invention is to provide an apparatus wherein the same tubular components employed for irrigating are provided with means intended for measuring the humidity of soil. A further object of the invention is to provide users with a simple technique for locating tubular components which are damaged following breakages or only partially functioning because of the obstruction of the dripping wings.

A further object of the invention is to provide the users with an apparatus for measuring soil humidity suitable for ensuring high level of resistance and reliability over time, also such as to be easily and inexpensively constructed.

These and yet other objects are achieved by the apparatus for measuring soil humidity of the present invention according to the main claim.

The construction and functional features of the apparatus for measuring soil humidity of the present invention shall be better understood from the following detailed description, wherein reference is made to the annexed drawing tables showing a preferred and non-limiting embodiment thereof, wherein:

figure 1 schematically shows a longitudinal section of a part or trunk of a linear duct of the apparatus for measuring soil humidity according to the present invention;

figure 2 shows a schematic cross section view along line D-D of figure 2 of the same part or trunk of duct;

figure 3 schematically shows a side view of a line joint suitable to connect to each other two parts or trunks of a linear duct of the apparatus of the present invention;

figure 4 schematically shows a longitudinal section of the line joint of figure 3; figure 5 shows a schematic cross section view along line B-B of figure 4 of the same line joint;

figure 6 shows a schematic cross section view along line C-C of figure 4 of the same line joint;

figure 7 shows a schematic cross section view along line A-A of figure 4 of the same line joint;

figure 8 schematically shows a longitudinal section of the assembly formed by a line joint and two trunks of a duct coupled one to the other and in operative conditions;

figure 9 schematically shows a longitudinal section of a derivation or "T" joint of the apparatus for measuring soil humidity according to the present invention;

figure 10 schematically shows a longitudinal section of a line joint provided with a power supply plug of the apparatus of this invention; figure 11 schematically shows a longitudinal section of a closing cap of the trunks or ducts of the apparatus according to the present invention; figure 12 schematically shows a longitudinal section of the same cap provided with terminal resistance;

figures 13 and 14 schematically show the same number of possible installations of the apparatus of the present invention.

With initial reference to figures 1 and 2, the apparatus for measuring soil humidity of this invention comprises a number of tubular elements or trunks (10) which, suitably connected one to the other as clarified hereinafter, form a network of ducts, buried at a depth preferably comprised between 10 and 80 centimetres according to the kind of crop. The tubular elements 10, having suitable section and length may be formed through extrusion of rigid or flexible plastic material. To said tubular elements 10 are coupled linear joints, shown in figures 3, 4, 8 and 10, "T" joints shown in figure 9, as well as end caps shown in figures 11 and 12. Said linear joints, "T" joints and end caps are made of rigid plastic material.

According to a first feature of the invention, the tubular elements 10 incorporate in the wall thereof two electric cables 12, 14 preferably developed in diametrically opposed position; the electric cables 12, 14, advantageously devoid of insulating sheath, are made of copper or conductive metal material and are buried in the thickness of the walls of the tubular elements 10 upon performing the extrusion of the elements thereof. The opposed ends of the electric cables 12, 14 are aligned to the respective heads of tubular elements 10 wherein said cables are inserted. The apparatus of the present invention comprises, furthermore, linear joints 16 and 16', schematised in detail in figures 3, 4, 8 and 10 as well as "T" joints 18, one of which schematised in figure 9 and end caps 20, 22, all of them suitable to be fitted on the ends of the tubular elements 10. According to a further specific feature of the invention, the linear joints 16 and 16', the "T" joints 18 and the caps 20, 22 comprise means apt to guarantee the continuity of the cables 12, 14, therefore the continuity of the electric connection in the apparatus of the invention. Said means advantageously consist of conductive foils developed according to a continuous and discontinuous spiral-wise pattern indicated with reference numeral 24 in figures 3, 4, 7 and from 8 to 10. The metal conductive foils 24 have a substantially triangular profile with a sharp and cutting edge and extend along the lateral outer surface of the opposed end zones of said joints 16, 16', 18 and caps 20, 22. The foils thereof are integral to opposed filaments 12', 14' integrated in the thickness of the wall of the joints 16, 16', 18 and caps 20, 22 upon the forming thereof, which is performed through thermal moulding. The foils 24 are preferably made of copper, likewise the filaments 12', 14' wherefrom they extend. The extension or outwards projection of the foils 24 is such as to allow them to abut the electric cables 12, 14 of tubular elements 10 when said latter are coupled to joints 16, 16', 18 and/or caps 20, 22. Said coupling is typically performed through a manual operation of substantial screwing. In consideration of the fact that the tubular elements 10 have the same or slighdy bigger diameter than the end of linear joints 16 and 16', the screwing is performed by forcing the end of said linear joints to fit in the flexible tubular element 10 which therefore defines respective portions 26 wherein the diameter is increased. This peculiarity allows in the same way also the easy coupling of the "T" joints 18 and of the caps 20, 22 to the tubular elements 10. Said joints 16, 16', 18 and caps 20, 22 may be provided with integral annular projections, continuous or discontinuous, forming the same number of abutments of the tubular elements 10. The hydraulic seal of the connections between the different components of the apparatus of the invention is achieved by mechanical interference, but it cannot be excluded in any case the possibility to employ suitable gaskets, for example O-Rings, arranged in grooves formed on the joints 16, 16', 18, or on the caps 20, 22 and/or on the tubular elements 10, or, moreover, to further tighten the tubular elements 10 on the joints 16, 16', 18, or on the caps 20, 22 by means of a tightening nut. Furthermore, it cannot be excluded the possibility to employ suitable gaskets, for example O-Rings, arranged in grooves formed on the joints 16, 16', 18, or on the caps 20, 22 and/or on the tubular elements 10, for insulating the foils 24 from the fluid circulating in the apparatus forming the irrigation network. During the tightening the foils 24, made of metal material, cut the thickness of the coating of the tubular element 10 covering the electric cables 12 inside the element thereof, in order to guarantee the continuity of the electric signal between two consecutive tubular elements through the filaments 12' and 14'. The tubular elements 10, the joints 16, 16', 18, and the caps 20, 22 are advantageously provided on the outside with a coloured trace in correspondence of the cables 12 and 14 in the case of the tubular elements 10 and in correspondence of the filaments 12' and 14' in the case of the joints 16, 16' and 18 and of the caps 20, 22. The alignment of the coloured traces of the tubular elements with the traces of the linear joints, the "T" joints and of the caps at the end of the screwing guarantees the alignment of the electric cables 12 and 14 with the filaments 12' and 14' and, therefore, the continuity of the electric signal obtained through the foils 24.

Figure 10 shows by way of an example at least a further linear joint, globally indicated with reference numeral 16', provided with an electric supply plug. According to this solution, the joint 16' is provided with an integral tubular expansion or extension 30, vertically oriented, whereto arrive respective derivations or terminations of the filaments 12', 14'. The ends of said derivations are electrically powered, for example through a cap 32 screwed to the tubular expansion 30. In this way on joint 16' may be applied an instrument for measuring the variation in the dielectric constant of the soil, with said electric cables representing the measurement probe connected to the wave generator and the signal analyser of the TDR system for example the PicoScope 5203, produced and distributed by Pico Technology, James House, Marlborough Road, Colmworth Business Park, PE19 8YP, Eaton Socon, St Neots, Cambridgeshire, United Kingdom.

The caps shown in figures 11 and 12 are respectively short-circuited and provided with electric resistance 34 according to alternative solutions. Obviously in the case which it results advantageous to keep the terminals of the electric cables 12 and 14 open, it would be sufficient to employ a cap devoid of the filaments 12' and 14'.

Examples of configurations of the development of the apparatus of the present invention are schematically shown in figures 13 and 14. Figure 13 defines a solution wherein the difference in potential is given between the electric cables of the same duct in this case a measure of the soil humidity locaHzed in the proximity of the roots of the plants shall be obtained. In the configuration of figure 14, on the other hand, the difference in electric potential is given between the electric cables of two ducts or contiguous lines, allowing the sampling of humidity at a higher depth. This last configuration may be advantageously employed when the sub-irrigation ducts are arranged staggered respect to the plant rows. As can be noticed from the above, the advantages achieved by the invention are clear.

The apparatus of the invention allows to measure in a direct way the average water content in the soil around the irrigation duct, therefore in correspondence of the root apparatus of the single plants and not in a punctual way. Water consumption may be therefore optimized, substantially reducing useless waste.

Although the invention has been described hereinbefore with particular reference to an embodiment thereof made by way of a non-limiting example, several changes and variations shall clearly appear to a man skilled in the art in the light of the above description. This invention, therefore, is intended to include any changes and variations thereof falling within the spirit and the scope of protection of the following claims.

For example, the apparatus may comprise mixed-linear and curvilinear elements, having the same features of the tubular elements 10 and/or of the joints 16, 16', 18 or of the caps 20, 22.

Claims

1) An apparatus for measuring soil humidity, employable in irrigation systems that provide buried pipes made of plastic material and especially in drip sub-irrigation systems, comprising a network of ducts consisting of buried rectilinear or mixed-linear development pipes, rectilinear or "T" joints, caps and eventual curvilinear elements, made of rigid or flexible plastic material of whatever suitable section, characterised in that it comprises a number of tubular elements (10) incorporating two electric cables (12-14) in conductive metal material, and are associated to rectilinear (16, 16¹) or "T" (18) joints and to end caps (20-22) apt to guarantee the electric continuity of said apparatus.

2) The apparatus according claim 1, characterised in that the electric cables (12-14) are made in copper devoid of insulating sheath and are buried in the thickness of the walls of the tubular elements (10), in a reciprocal diametrically opposed position, upon forming through extrusion of the said tubular elements.

3) The apparatus according to claim 1, characterised in that said means apt to guarantee the electric continuity of the apparatus thereof consist of conductive metal foils (24) integral to filaments (12'-14') integrated in opposite position in the thickness of the wall of the rectilinear (16) joints, the "T" joints (18) and in the caps (18-20) upon forming thereof through thermal moulding of rigid plastic material. 4) The apparatus according to claim 3, characterised in that the filaments (Ι^-Ή¹) and the foils (24) integral thereto are made in copper, said foils having a substantially triangular profile with a sharp and cutting edge and extend along the lateral outer surface of the opposed end zones of said joints (16, 16', 18) and caps (20- 22) with continuous and discontinuous spiral-wise pattern.

5) The apparatus according to claim 1, characterised in that the opposed heads of the tubular elements (10) have respective sections (26) with a higher diameter than the remaining body that seat the corresponding ends of the rectilinear (16, 16*) or "T" joints (18) or of the caps (20-22).

6) The apparatus according to claim 1, characterised in that the rectilinear (16, 16") or "T" joints (18) and the caps (20-22) comprise continuous or discontinuous integral annular projections (28) forming the same number of abutments of the tubular elements (10).

7) The apparatus according to claims 1 and 3, characterised in that the tubular elements (10), the joints (16-16'-18) and the caps (20- 22) are provided on the outside with a coloured trace in correspondence of the cables (12-14) and of the filaments (12'- 14").

8) The apparatus according to claims 1 and 3, characterised in that the tubular elements (10), the joints (16-16'-18) and the caps (20- 22) are provided with seats or grooves for gaskets insulating the foils (24) from the fluid circulating in the apparatus thereof, forming the irrigation network.

9) The apparatus according to claim 1, characterised in that it comprises at least a joint (16*) provided with an integral tubular extension (30) vertically oriented, whereto are led the terminations of the filaments (12 -14) which are connected to an electric source through a cap (32) constrained to said extension (30) through threading or equivalent means.

10) The apparatus according to claim 7, characterised in that to the extension (30) of the joint (16*) is electrically connected an instrument for measuring the variation in the dielectric constant of the soil along or below which the apparatus thereof is installed.

11) The apparatus according to claim 1 characterised in that the caps (20-22) are short-circuited or provided with electric resistance (34).